In the heat treatment of lengths of textile material in a tensioning machine, in addition to maintaining the material at a suitable temperature and for a sufficient period of dwell time, it is important that optimum tensioning of the lengths of textile material across their width (that is to say in a direction at right angles to the transport direction) is always ensured. In this connection, it should be borne in mind amongst other things that varying alterations in width and thur alterations in the transverse tension can occur over the length of the heat treatment section in the tensioning machine as a result of the selected temperature and transit time and as a function of the type of textile material undergoing treatment. In order to be able to control the widthwise material tension within the length of textile material according to a desired overall tension, various machine constructions have already been developed in which the spacing of the two continuously moving tensioning chains which hold a length of material on its longitudinal edges is set with the aid of at least one transverse width-adjusting spindle.
This type of construction is described in German Offenlegungsschrift No. 2,335,124. Here the width-adjusting spindle consists of two half spindles with threaded sections, the threaded section of one half spindle being threaded in the opposite direction to that of the other half spindle so that when the width-adjusting spindle rotates in one direction or the other the guide rails for the tension chains, which are held on the half spindles by means of threaded nuts, can be moved towards or away from each other. While one half spindle is axially fixed and provided with a spindle drive, the second half spindle is axially movable but connected to the first half spindle so as to be rotationally fixed. The outer end of this second half spindle is extended towards the outside by a rod and is there articulated on a forked one-arm control lever, the lower free end of which is articulated on the piston rod of a pneumatic or hydraulic cylinder and which in its central region cooperates with one or two control switches in such a way that the spindle drive motor arranged at the opposite end of the width-adjusting spindle can be actuated to create a greater or smaller distance between the chain guide rails or tensioning chains so that a maximum permissible or minimum necessary widthways tension can be maintained. The working pressure of the pnuematic or hydraulic operating cylinder should be a criterion for the textile material tension provided.
In a practical construction of the known tensioning machine described above, the control provided there for the heat treatment of carpet lengths and the like may be sufficiently accurate; however, in tensioning machines for other textile finishing processes, particularly for lengths of more delicate textile materials, e.g. tulle, curtains, material for outer clothing, or industrial fabrics, the control provided in order to maintain a desired widthwise tension must be capable of being effected with considerably greater precision than is described above. In addition this known construction involves comparatively high construction costs and requires a correspondingly large amount of space.
The object of the invention, therefore, is to provide a tensioning machine which has a simple, space-saving construction and is distinguished by an extremely sensitive control for the widthwise tensioning of the length of material.